A benzylation of aldehydes using primary and secondary benzylboronic acid pinacol esters is reported. Activation of the boronic ester with s-butyllithium rendered it nucleophilic toward aldehydes. The activated nucleophile chemoselectively transfers the benzyl group over the s-butyl group, providing excellent yields of the benzylated products. 11B NMR experiments were performed to study the mechnism of this transformation.
Benzylation reactions of N‐tosylimines and N‐tert‐butanesulfinyl imines using benzylboronic acid pinacol ester are reported. s‐Butyllithium was used to activate the boronic ester, rendering it nucleophilic. The reaction was compatible with electronically diverse substituents on the imine in both substrate classes. Good diastereoselectivity was observed in additions to N‐tert‐butylsulfinylaldimines. The diastereoselectivity observed in these reactions is consistent with an open transition state for the addition. Examples of a secondary alkylboronic ester nucleophile and a N‐tert‐butanesulfinyl trifluoromethylketimine electrophile are also included.
Chiral cyclooctadiene (COD) derivatives are readily prepared
by
rhodium-catalyzed allylic C–H functionalization of COD. Either
mono- or difunctionalization of COD is possible generating the products
in high yield, diastereoselectivity and enantioselectivity. The double
C–H functionalization generates C
2-symmetric COD derivatives with four new stereogenic centers in >99%
ee, which can be readily converted to a series of chiral COD ligands.
Preliminary evaluations revealed that the COD ligands can be used
in rhodium-catalyzed asymmetric arylation of cyclohex-2-enone, leading
to the conjugate addition products in up to 76% ee.
Allylic C–H functionalization catalysed by group 9 Cp* transition-metal complexes has recently gained significant attention. These reactions have expanded allylic C–H functionalization to include di- and trisubstituted olefins, and a...
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